As European cities increasingly rethink the relationship between urban infrastructure and the natural environment, street lighting is emerging as a strategic tool for balancing public safety with biodiversity protection. The case of Gladsaxe, Denmark, where red lighting has been introduced to protect bat populations, illustrates how even seemingly ordinary urban systems can become part of a broader ecological transformation
The transformation of urban infrastructure in the twenty-first century increasingly requires cities to move beyond purely human-centered engineering models and toward a more integrated understanding of how built environments interact with ecological systems, biodiversity corridors, and the rhythms of non-human life. In this context, the decision by the Danish municipality of Gladsaxe, located near Copenhagen, to replace traditional white street lighting with red-spectrum illumination along a section of Frederiksborgvej represents far more than an isolated technical intervention; it reflects a profound shift in how contemporary cities are beginning to redefine the relationship between mobility, environmental responsibility, and urban design. What might initially appear to be a merely aesthetic change is, in reality, a sophisticated response to one of the most underestimated dimensions of Smart City development: the ecological consequences of artificial light at night.
The Ecological Logic Behind the Use of Red Light
Artificial nighttime lighting has long been considered an unquestioned component of urban safety, road infrastructure, and public space management. However, over the last decade, research in urban ecology and environmental engineering has demonstrated that the spectral composition of street lighting can significantly alter the behavior of nocturnal species, particularly bats, insects, birds, and certain amphibians. In the case of Gladsaxe, the intervention was specifically designed to protect several species of roosting and foraging bats that inhabit the green corridors adjacent to Frederiksborgvej, an area where ecological activity had been previously documented at high levels.
The technical rationale is rooted in wavelength behavior. Traditional cool white LED lighting, which contains a high proportion of blue-rich short wavelengths, tends to be significantly more disruptive to nocturnal wildlife, often creating what environmental scientists describe as “light barriers,” spaces that animals avoid crossing because they become exposed to predators or experience disorientation. By contrast, red-spectrum light operates at a longer wavelength and has been shown to interfere far less with the movement and feeding behavior of many bat species. This makes it possible to preserve essential urban visibility while minimizing ecological fragmentation.
In fact, the Gladsaxe project was implemented along a 700-meter stretch of road and cycle infrastructure, where approximately 30 low-height bollards were installed at intervals of 30 meters, intentionally leaving dark corridors between them so that light-sensitive bats could continue crossing the area safely. Additional higher poles were placed only at crossing points to improve pedestrian and cyclist awareness.
A Practical Example of Infrastructure Designed for Multi-Species Urbanism
What makes this case particularly significant from an urban transformation perspective is that it introduces a practical model of what may be called multi-species infrastructure planning, in which roads, pathways, and public lighting systems are no longer optimized exclusively for human circulation but are also designed around ecological continuity.
A highly relevant practical example can be observed in how the municipality balanced the needs of cyclists using the Farum cycle superhighway with the protection of nearby bat colonies. Rather than eliminating lighting altogether, which would have compromised public safety and active mobility objectives, planners opted for a calibrated lighting solution that satisfies minimum visibility standards while reducing environmental stress. This is precisely the kind of design logic increasingly associated with advanced Smart City strategies, where infrastructure becomes adaptive, contextual, and evidence-based.
Moreover, this intervention aligns with broader European experimentation in biodiversity-sensitive lighting. Similar approaches have been developed in locations such as Zuidhoek-Nieuwkoop in Netherlands, recognized as one of the first villages to install red LED systems specifically intended to protect bats, and in selected wildlife corridors in the United Kingdom, where illuminated crossings have been adapted to support nocturnal fauna movement.
The Tension Between Biodiversity and Road Safety
Nevertheless, the adoption of red lighting is not without debate. One of the most important technical and policy discussions emerging from this type of intervention concerns road safety and human visual perception. White light generally offers superior color rendering and contrast sensitivity, which are critical variables for nighttime driving, obstacle detection, and reaction times.
This introduces a strategic dilemma for urban planners: how to preserve ecological integrity without compromising traffic safety, especially in mixed-use corridors where vehicles, bicycles, and pedestrians coexist. The Gladsaxe case is particularly valuable because it does not present red lighting as a universal replacement model, but rather as a site-specific solution applied in ecologically sensitive zones.
This distinction is crucial. The future of sustainable urban lighting will likely not be based on one standardized system, but on adaptive zoning models, where light intensity, color temperature, and spectral composition vary according to urban function, biodiversity sensitivity, and temporal conditions. For example, amber or red light may be used near parks, forests, river corridors, and ecological buffers, while neutral white lighting remains appropriate in high-density traffic areas.
A New Paradigm for Smart and Sustainable Cities
What ultimately emerges from this Danish case is a broader transformation in urban thinking. Cities are beginning to recognize light pollution as a critical environmental issue, comparable in strategic relevance to air quality, noise pollution, or heat island effects.
In Smart City terms, this represents a major conceptual evolution: infrastructure is no longer evaluated solely through efficiency metrics such as illumination coverage or energy consumption, but also through its impact on ecosystems, species movement, and biodiversity resilience. This perspective aligns directly with the goals of sustainable urban development and with the ecological ambitions embedded in European urban policy frameworks and the UN Sustainable Development Goals, particularly SDG 11 and SDG 15.
The Gladsaxe experiment therefore offers a compelling model for future cities: urban infrastructure that is technologically advanced, environmentally intelligent, and designed not only for humans, but for the broader living systems with which cities coexist.